Insulated electric cable having an external semiconductive layer

ABSTRACT

An insulated electric cable having an external semiconductive layer with easy stripping qualities for termination wherein the cable is insulated primarily with crosslinked polyethylene or a crosslinked polyethylene copolymer and the external semiconductive layer consists of an ethylene vinyl acetate copolymer containing 25-55 wt-percent vinyl acetate and 2,5dimethyl-2&#39;&#39;,5&#39;&#39;-di(tertiary butyl/peroxy)-hexine-3 and an inclusion of an electric conductive substance such as carbon black to render the layer semiconductive.

United States Patent 91 Miyauchi et a1.

[451 March 6, 1973 1 INSULATED ELECTRIC CABLE HAVING AN EXTERNAL SEMICONDUCTIVE LAYER [75] lnventors: Hirokazu Miyauchi; I-Iironaga Matsubara, both of Osaka, Japan [73] Assignee: Sumitomo Electric Industries, Ltd.

Osaka, Japan [22] Filed: Oct. 5, 1970 [21] Appl. No.: 77,918

[52] US. Cl...174/l20 SC, 174/105 SC, 174/110 PM [51] Int. Cl. ..H0lb 9/02 [58] Field of Search...174/36, 120 R, 120 SC, 102 R,

174/102 SC, 105 SC, 106 SC, 110 PM, 107,

[56] References Cited UNITED STATES PATENTS 3,259,688 7/1966 Towne et a1. 1 74/127 X 3,441,660 4/1969 Garner 174/1 10 PM X 3,472,692 10/1969 Setsuya lsshiki ..l74/l06 SC UX 3,433,891 3/1969 Zysk et a1 ..l74/l02 SC X 3,287,489 12/1966 Huizd, Jr.

3,096,210 7/1963 Boonstra ..l74/l 10 PM UX FOREIGN PATENTS OR APPLICATIONS 1,103,099 2/1968 Great Britain ..174/102 SC OTHER PUBLICATIONS The Condensed Chemical Dictionary 6th Ed., Reinhold 1961, p. 395. (QD 5 C5 1961 c.12)

Primary ExaminerBernard A. Gilheany Assistant ExaminerA. T. Grimley Attorney-Carothers and Cal-others [5 7] ABSTRACT An insulated electric cable having an external semiconductive layer with easy stripping qualities for termination wherein the cable is insulated primarily with crosslinked polyethylene or a crosslinked polyethylene copolymer and the external semiconductive layer consists of an ethylene vinyl acetate copolymer containing 25-55 wt-percent vinyl acetate and 2,5-dimethyl-2',5'-di(tertiary butyl/peroxy)-hexinc-3 and an inclusion of an electric conductive substance such as carbon black to render the layer semiconductive.

7 Claims, .1 Drawing Figure INSULATED ELECTRIC CABLE HAVING AN EXTERNAL SEMICONDUCTIVE LAYER This invention relates to an insulated cable having an external semiconductive layer, and more particularly to the structure of an insulated cable having an insulation primarily consisting of crosslinked polyethylene or a crosslinked polyethylene copolymer, having an external semiconductive layer.

In the conventional art, when covering the insulating layer of a crosslinked polyethylene insulated cable with an extruded semiconductive layer, wherein low density polyethylene, a copolymer of ethylene and vinyl acetate or a polymer consisting mainly of these substances is used as the base of the insulation layer, to which are further added talc, clay, calcium carbonate and like inorganic fillers, various age resistors, processing aids and the like as required, it is a usual practice to use a composition such as a mixture of a copolymer of ethylene and ethyl acrylate, with dicumyl peroxide and the like AD crosslinking agents and electrio-conductive carbon black, or a mixture of a copolymer of ethylene and vinyl acetate, with dicumyl peroxide and the like crosslinking agents, and electricconductive carbon black for the semiconductor outer layer.

polyethylene insulated cable having the external semiconductive layer, it is necessary to remove the semiconductive layer of the cable for a certain length from the end thereof. The removal of the semiconductive layer should be complete in this case, and in removing it the insulating layer should be left intact. In recent years, through the development of the art, parts and accessories premolded to the shape of cable joints and terminations have come in handily for the splicing and terminating of crosslinked polyethylene insulated cable having an external semiconductive layer. This method gives a more stable quantity and facilitates a more speedy operation as compared with the conventional treatment methods of wrapping with a tape, heat molding and like means, and the above method is now widely used. In this method, however, it is required that the premolded accessories used should be fitted to the contour ofthe cable without allowing any electrical faults to exist therebetween. Thus demands are growing for a method to easily strip off the semiconductive layer without damaging the insulating layer in a short period of time than heretofore possible.

When the conventional compositions as abovementioned are used to cover the insulated layer, it is hard and takes time to first strip off the semiconductive coating, and the insulation layer easily marred. Thus none of these compositions satisfy the abovementioned requirements.

The present invention, however, is intended to provide a crosslinked polyethylene insulated cable having a semiconductive layer which can be easily stripped off without leaving a fraction of the semiconductive layer on the surface of the insulating layer nor marring the insulating layer.

The present invention pertains to' a crosslinked polyethylene insulated cable having a semiconductive layer which is extruded over the insulating layer, and provides the cable with a semiconductive layer which can be easily stripped off. This semiconductive layer is formed by extruding a composition obtained by mixing When splicing and treating the end of a crosslinked a copolymer of ethylene and vinyl acetate, containing 25-55 wt percent vinyl acetate and desirably in a range, in excess of 0.2 but less than 6.0 wt. parts of 2,5- dimethyl-2, 5-di(tertiary butyl peroxy)-hexene-3 in respect of 100 wt. parts of said polymer, and an electric conductive substance.

lf required, age resistors, processing aids and the like may be further added thereto according to the operation conditions.

As the result of researches by the inventors it has been confirmed that the amount of carbon black (25-70 wt. parts based on 100 wt. parts of the polymer), amine-, or phenol-based age resistors and zinc stearate and the like processing agents do not affect the ease of stripping off the semiconductive layer.

An example of the insulated cable having the external semiconductive layer of the invention is shown in FIG. 1, wherein, the cable consists of the conductor 1, internal semiconductive layer 2, insulating layer 3 and external semiconductive layer 4.

Examples of the invention, examples for reference and examples for comparison will be given hereinafter, in which different materials as mentioned hereinafter were used.

A stranded conductor having a sectional area of 100 mm was covered with an ordinary extruded semiconductive layer, over which the insulating layer and semiconductive layer as shown in Table l were extruded in succession to cover the cable, and the product was completely crosslinked in a saturated water vapor under an atmospheric pressure of 15 atmospheres.

Incisions, 10 mm wide and running in the axial direction of the cable, were made in the external semiconductive layer covering the surface of the cable, and the cable was subjected to a peeling test by a tension tester, results of which are also shown in Table l.

The semiconductive layers in the table respectively contained wt. parts of acethylene carbon black, 1 wt. part of age resistor and 1 wt. part of zinc stearate, all based on 100 wt. parts of the base polymer, but the type and amount of the crosslinking agents and the thickness of the semiconductive layer were varied.

As is evident from the examples, only when an ethylene vinyl acetate copolymer containing 25-55 wt percent vinyl acetate and 2,5-dimethyl-2,5'-di-(tertiary butyl peroxy)-hexine-3 are combined is the desired semiconductive layer of the present invention obtained, one which can be easily stripped off the base insulation of crosslinked polyethylene copolymer.

If the content of vinyl acetate is less than 25 wt. percent of the ethylene vinyl/acetate copolymer, the layer will not be stripped off easily, and if it exceeds wt. percent, its adhesion to the insulating layer will be impaired, making the cable unfit for use. When the content of vinyl acetate of the EVA copolymer is 25-55 wt. percent the layer can be stripped off with utmost ease.

When the content of 2,5-dimethyl-2',5'-di(tertiary butyl peroxy)-hexine-3 is less than 0.2 wt. part based on wt. parts of said copolymer, the peeling strength of the semiconductive layer is relatively low, and if it exceeds 6 wt. parts the adhesion of the semiconductive layer to the insulating material is impaired, also reducing the applicability of the cable. A range, in excess of 0.2 but less than 6 wt. parts, exhibits the best results.

As regards the thickness of the layer, if the thickness of the semiconductive layer extruded over the insulat- TABLE 1 Semieonrluctive layer (over insulating layer) Crosslinking Thickness No. Insulating layer Base polymer agent (mm.) Peeling strength (kg/ mm.)

Reference Polyethylene Sp. gr.=0.92 g./cc., EVA1, \'A=15%, i=6 X2, 1%... 0. 5 More than 5, and left on "-3 MI=2, "-4 DCP=2.0%, insulating layer.

age resistor=0.2%. Example 1 Same as Reference 1 EVA, VA=%, 1:0 X, 1%....... 0.5 3.0. Example 2. ..do EVA, \"A=35%, Ml=6 X, 1%... 0.5 3.5. Example 3... EFA, VA=50%, 511:0. X,1 0.5 2. Reference 2 ..do Same as Example .2 Nil 0. 5 Semiconduetive layer torn so not stripped 011'. Reference 3 ..do ..do X, 0.2 0.5 Do. Example 4... X, 0.3 0.5 3.5. Example 5. X, 0.5 0. 5 3.5. Example 6. X, 1.0 0.5 3.5. Example 7... X, 6.0 0. 5 3.0. Reference 4. X, 0.0 0. 5 0.3. Reference 5 lo X, 1.5 0.1 .umiconduetive layer torn so not stripped 011. Example 8 ..d0..... .(lo X, 1.5%... 0.2 3.3. Exampleil (l0 X, 1.5%... 0.5 3.4. Example 10. X, 1.5%.. L0 3.3. Example 11..... 2 2.0%..... 0.7 3.5

0%, age reg tor=0.2%. Example 12..... Composition of Example 11: 100 ...do X, 2.0%... 0. 7 3.0.

Wt. parts plus talc: wt. parts. Example 13..... Composition of Example 12: 100 ..do X, 2 0%... 0. 7 3.1.

wt. parts plus clay 30 wt. parts. Example 14"... EVA, VA=16%, MI=3,DCP= .(lo X, 1.5%..... 1.1] 4.3.

2%, A.R.=0.2%. Example 15..... Composition of Example 14: 100 ..do X, 1.6%... 1. 0 3.0.

wt. parts plus talc 30 wt. parts. Comparison 1... Same as Refereneel ..do DCP, 1.0%. 0.5 More than 5, and left on insulat- 1111,! ayer. Comparison 2 ..d0 lo D01, 5.0% 0. 5 D0. Comparison 3 ..do Same as Example 2 except EVA X, 1.0%..... 0.5 Do.

was replaced with l) lD-(ilGJ.

Example 16 ..do EVA, \'A=35%, Ml=l X, 1%..... 0.5 3.5. Example 17. .(lo. EVA, \"A=50%, X, 0.5 3.5. Example 18 ..(lo EVA, VA=50%, IM=60 X,1%...... 0.5 2.

*-1 EVA=Eth1ene vinyl acetate copolymer; \'A=amount ofvinyl acetate in copolymer.

ing layer is less than 0.1 mm, the layer, when stripped, will easily tear off, and it should be desirably more than 0.1 mm.

Thus, only when an ethylene vinylacetate copolymer containing 25-55 wt. tpercent vinyl acetate, and a range in excess of 0.2 bu less than 6 wt. parts, of 2,

It was also confirmed when said crosslinking agent,

2,5-di-methyl-2',5-di(tertiary butyl peroxy)-hexinc-3 is .added to a high molecular polymer other than ethylenevinylacetatc copolymer, excellent effects can not be expected. Only by the use of the composition of the invention, can the semiconductive layer, which can be effectively stripped off, be obtained. The amount of carbon black is not particularly limited, but if it is less than 25 percent, the electric conductivity as required in the invention can not be obtained while an amount exceeding 70 percent will deteriorate the mechanical proparties of the conductive layer, itself, impairing workability thereof, so that a range of 25-70 percent is desirable.

The present invention can be, of course, applied to electric cables having a insulating layer whose principal component is crosslinkcd polyethylene or crosslinked polyethylene copolymer, irrespective of the size and use of the cable.

"- 5 l)ll)616U=Ethyleneethylaerylate copolynn-rof UCC, USA.

What we claim is:

1. An insulated electric cable having an external semiconductive layer extruded over the insulating layer thereof comprising a cable insulated primarily with an insulation selected from the group consisting of crosslinked polyethylene and crosslinked polyethylene copolymer, and an external semiconductivc layer consisting of an ethylene vinyl acetate copolymer containing 25-55 wt. percent vinyl acetate and 2,5-dimethyl- 2,5'-di(tertiary-butyl/peroxy)-hexine-3 and an inclusion of an electric conductive substance.

2. An insulated cable as claimed in claim 1, wherein the insulating layer is made of crosslinked polyethylene.

3. An insulated cable as claimed in claim 1, wherein the insulating layer is made of a crosslinked polymer consisting of a copolymer of ethylene and vinyl acetate.

4. An insulated cable as claimed in claim 1, wherein inorganic filler is added to the insulating layer thereof.

5. An insulated cable as claimed in claim 1, wherein a range, in excess of 0.2 but less than 6 wt. parts, of 2,5- dimethyl-2',5'-di-(tertiary butyl/peroxy)-hexine-3, based on wt. parts of said ethylene vinyl acetate copolymer is contained in the semiconductive layer.

6. An insulated cable as claimed in claim 1, wherein the thickness of the external semiconductive layer is more than 0.1 mm.

7. An insulated cable as claimed in claim 1, wherein 25-70 wt. parts of carbon black based on 100 wt. parts of said copolymer is contained in the external semiconductive layer. 

1. An insulated electric cable having an external semiconductive layer extruded over the insulating layer thereof comprising a cable insulated primarily with an insulation selected from the group consisting of crosslinked polyethylene and crosslinked polyethylene copolymer, and an external semiconductive layer consisting of an ethylene vinyl acetate copolymer containing 25-55 wt. percent vinyl acetate and 2,5-dimethyl-2'',5''-di(tertiary-butyl/peroxy)-hexine-3 and an inclusion of an electric conductive substance.
 2. An insulated cable as claimed in claim 1, wherein the insulating layer is made of crosslinked polyethylene.
 3. An insulated cable as claimed in claim 1, wherein the insulating layer is made of a crosslinked polymer consisting of a copolymer of ethylene and vinyl acetate.
 4. An insulated cable as claimed in claim 1, wherein inorganic filler is added to the insulating layer thereof.
 5. An insulated cable as claimed in claim 1, wherein a range, in excess of 0.2 but less than 6 wt. parts, of 2,5-dimethyl-2'',5''-di-(tertiary butyl/peroxy)-hexine-3, based on 100 wt. parts of said ethylene vinyl acetate copolymer is contained in the semiconductive layer.
 6. An insulated cable as claimed in claim 1, wherein the thickness of the external semiconductive layer is more than 0.1 mm. 